1. Field of the Invention
The present invention relates to an organic light emitting display (OLED) device, and more particularly, to an OLED device in which demultiplexers supply data signals using double data lines in order to secure sufficient time to supply the data signals to the data lines and transmit the data signals to pixels.
2. Description of the Related Technology
Recent years have seen considerable research into flat panel displays (FPDs) because they can be made smaller and lighter than display devices using cathode ray tubes (CRTs). Among the FPDs, an organic light emitting display (OLED) device has attracted much attention as the next-generation FPD because of excellent luminance and viewing angle characteristics.
Unlike a liquid crystal display device (LCD), the OLED device needs no additional light source and makes use of a light emitting diodes that emit certain colors of light. The light emitting diode emits light with brightness corresponding to the amount of driving current that is supplied to an anode electrode.
FIG. 1 is a schematic diagram of a conventional OLED device.
The OLED device includes a pixel portion 10, a scan driver 20, a data driver 30, and an emission driver 40.
The scan driver 20 sequentially supplies scan signals to scan lines S1-Sn in response to scan control signals (i.e., a start pulse and a clock signal) output from a timing controller (not shown).
The data driver 30 supplies data voltages corresponding to red (R), green (G), and blue (B) data to data lines D1-Dm in response to data control signals output from the timing controller.
The emission driver 40 comprises shift registers and sequentially supplies emission control signals to emission control lines E1-En in response to a start pulse and a clock signal output from the timing controller.
The pixel portion 10 includes a plurality of pixels P11-Pnm, which are located in regions where a plurality of scan lines S1-Sn and a plurality of emission control lines E1-En intersect a plurality of data lines D1-Dm. The pixel portion 10 displays an image according to an applied data voltage.
Each of the pixels P11-Pnm includes R, G, and B sub-pixels.
In the pixel portion 10, the R, G, and B sub-pixels have the same circuit construction and emit R, G, and B light with brightness corresponding to current supplied to each organic light emitting diode sub-pixel. Thus, each of the pixels P11-Pnm combines light emitted from the R, G, and B sub-pixels and displays a specific color according to the combination of sub-pixel color and brightness.
Such an OLED device requires three data driving circuits to supply data signals from the data driver 30 to three (R, G, and B) data lines connected to the pixel portion 10. However, it is difficult to provide the data driving circuits in a number equal to the number of the data lines due to the area of the panel and the fabrication cost. Also, as the number of pixels of the OLED device increases, the OLED device needs more data driving circuits.
FIG. 2 is a schematic diagram of the data driver of a conventional OLED device.
Referring to FIG. 2, the conventional OLED device includes a data driver 30 having demultiplexers 32.
The data driver 30 includes an m number of demultiplexers 32 and an m number of data driving circuits 31. The demultiplexers 32 supply data signals to data lines D1-Dk of a plurality of pixels P11-P1k of a pixel portion 10. The data driving circuits 31 are connected to the demultiplexers 32 and supply data signals to the demultiplexers 32, respectively.
Each of the data driving circuits 31 receives R, G, and B data from a timing controller (not shown), converts the data into an analog data signal, and supplies the data signal to a data output line DLm.
The data signal is sequentially supplied through the data output line DLm to an input terminal of the demultiplexer 32.
The demultiplexer 32 sequentially supplies the data signal to the pixels P11-P1k in response to a control signal output from the timing controller.
Accordingly, since the data signal is supplied from one demultiplexer 32 to k data lines D1-Dk, the number of the data driving circuits 31 is reduced to 1/k.
In such an OLED device, since a plurality of data lines D1-Dmk are formed on the pixels P11-Pnmk across the pixel portion 10, capacitors are formed. Accordingly, after the capacitor of the data line Dmk is charged with a predetermined electric charge corresponding to a data signal, the data signal is transmitted to a pixel P1mk. The operation of the conventional OLED device having the demultiplexer 32 includes supplying the data signal from the demultiplexer 32 to the data line Dmk and transmitting the supplied data signal to the pixel P1mk enabled by supplying a scan signal for a first horizontal period.
However, because this OLED device should supply the data signal to the k data lines D1-Dk and supply the scan signal to the pixel portion 10 for the first horizontal period, a time required for supplying and transmitting the data signal is not enough. When the data signal is supplied for an insufficient time, the capacitor of the data line Dmk is not fully charged with an electric charge corresponding to the data signal but has the electric charge in common with a storage capacitor of the pixel P1mk. Also, since there is not enough time to transmit the stored data signal to the pixel P1mk, electric charge corresponding to the data signal is not sent to the pixel P1mk. As a result, the OLED device does not emit light with brightness corresponding to the supplied data signal, and thus the image quality is poor.